This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from the inventor""s application PHOTODETECTOR DEVICE AND METHOD FOR MANUFACTURING THE SAME filed with the Korean Industrial Property Office on the day of Jul. 12, 1999 and there duly assigned Ser. No. 27990/1999.
1. Field of the Invention
The present invention relates to optoelectric devices and processes for manufacturing optoelectric devices. More particularly, the invention relates to photodetector devices, and processes for manufacturing photodetector devices, with relatively large photo-receiving areas that are capable of providing high-speed responses.
2. Description of the Related Art
Optical data communications such as optical interconnections, require optical signal sending and receiving units, such as light emitters that produce optical signals and photodetectors that detect the optical signals that have been generated by light emitters. As the need for high speed transmission increases, optical interconnections for communications through local area networks (LANs), computer-to-computer, computer-to-peripheral device, board-to-board, and chip-to chip, have replaced conventional copper wire.
To meet the requirement for high speed transmission, optical interconnection needs a rapidly responsive photodetector, which is characterized by a small photo-receiving area and low capacitance. Conventional P-I-N photodetectors tend to be integrated on a n-type substrate beginning with an n-type semiconductor layer, upon which an intrinsic (that is, an undoped) semiconductor layer and a p-type semiconductor layer are stacked in sequence. A meta annular p-electrode will be formed on the top of the p-type semiconductor layer, and an n-electrode may be formed on the back side of the substrate. With other designs of conventional P-I-N photodetectors, the P-I-N structure is implemented on the n-type substrate by diffusion.
One of the factors determining the capacitance of such a P-I-N photodetector is the characteristics of the materials used to construct the photodetector. For example, a P-I-N photodetector made of Si has even less capacitance than one formed of GaAs. The intrinsic semiconductor layer must be formed as thick as 10 to 20 xcexcm. because the indirect transition bandgap of Si reduces absorbency. Thus, for high speed response, a high voltage of 10V or more is needed. For this reason, a photodetector made of Si is inappropriate in application fields which need high speed response with a low voltage. In contrast, because GaAs has a direct transition bandgap, the intrinsic semiconductor layer can be formed to have a thickness of 2 to 4 xcexcm, and thus the photodetector is operable with a low voltage. The speed of response is limited however, because GaAs has a high dielectric constant; consequently the capacitance of the photodetector is high.
Another factor, which determines the capacitance of a photodetector, is the photo-receiving area. Capacitance is proportional to the photo-receiving area, and thus the capacitance can be lowered by reducing the photo-receiving area. When the photo-receiving area is reduced however, a lens for condensing incident light into a small photo-receiving surface is needed; this deleteriously increases the packaging cost, in addition to lowering the sensitivity of the device.
It is, therefore, an object of the present invention to provide an improved photodetector device and process for manufacturing photodetector devices.
It is another object to provide photodetector devices and processes for manufacturing photodetector devices with relatively large photo-receiving areas.
It is still another object to provide photodetector devices and processes for manufacturing photodetector devices that exhibit high speed responses.
It is yet another object to provide a photodetector device having a small capacitance and a high speed response even with a relatively large photo-receiving area, and a process for manufacturing the same.
It is yet another object to provide photodetector devices and processes having a high speed response without a concomitant increase in the packaging cost or a diminution of the sensitivity of the device.
According to one aspect of the present invention, a photodetector device is provided that may be constructed with a doped semiconductor substrate; an intrinsic semiconductor material layer formed over the substrate, for absorbing incident light; an upper semiconductor material layer doped with the opposite type to the substrate, formed on a portion of the intrinsic semiconductor material layer to allow at least a portion of the incident light to directly enter the intrinsic semiconductor material layer; an upper electrode formed in a predetermined pattern on the upper semiconductor material layer, the upper electrode electrically connected to the upper semiconductor material layer; and a lower electrode electrically connected to the substrate, wherein a portion of the intrinsic semiconductor material layer constitutes at least a part of a photo-receiving surface.
Preferably, the upper semiconductor material layer is formed only below the upper electrode. The upper semiconductor material layer may have a predetermined pattern on the photo-receiving surface. The photodetector device may further comprise a lower semiconductor material layer doped with the same type as the substrate, between the substrate and the intrinsic semiconductor material layer. Preferably, the substrate is formed of GaAs, InGaAs, or Si.
According to another aspect of the present invention, a process is provided for manufacturing a photodetector device, the process contemplates preparing a doped semiconductor substrate; forming an intrinsic semiconductor material layer over the substrate for absorbing incident light; forming an upper semiconductor material layer doped with the opposite type to the substrate, on a portion of the intrinsic semiconductor material layer through which at least a portion of the incident light directly enters the intrinsic semiconductor material layer, the portion of the intrinsic semiconductor material layer constituting at least a part of a photo-receiving surface; forming an upper electrode with a predetermined pattern on the upper semiconductor material layer, the upper electrode electrically connected to the upper semiconductor material layer; and forming a lower electrode electrically connected to the substrate.
Preferably, the upper semiconductor material layer is constructed by forming an upper semiconductor material layer over the intrinsic semiconductor material layer; and etching a portion of the upper semiconductor material layer, such that a portion of the surface of the intrinsic semiconductor material layer is exposed to serve as at least a part of the photo-receiving surface.
Preferably, the upper semiconductor material layer is etched to leave a portion of the upper semiconductor material layer being below the upper electrode. Preferably, the upper semiconductor material layer is etched to leave an upper semiconductor material pattern at the photo-receiving surface, and a portion of the upper semiconductor material layer being below the upper electrode. Preferably, between preparing the substrate and forming the intrinsic semiconductor material layer, the photodetector device manufacturing process further contemplates a step of forming a lower semiconductor material layer doped with the same type as the substrate, over the substrate.